High tension network distribution system

ABSTRACT

A high tension network distribution system which comprises high voltage feeders connected in a net-type for carrying electric power of commercial frequency, distribution transformers connected to said feeders, feeder breakers at the ends of said feeders adjacent to the associated substation therefor, protector breakers at the ends of said feeders adjacent to their feeding points, a carrier signal transmitter for applying zero-phasesequence carrier signals across said feeders and ground, an insulating transformer for transmitting said electric power of commercial frequency between adjacent feeders, but not for transmitting said carrier signal between the adjacent feeders, and signal receivers for receiving said zero-phase-sequence carrier signals from the feeders, said protector breakers including relay means for closing the corresponding breaker when the corresponding receiver receives the carrier signal and for opening the breaker when the receiver does not receive the carrier signal.

United States Patent [1 1 Oyachi [54] HIGH TENSION NETWORK DISTRIBUTION SYSTEM [75] Inventor: Toshio Oyachi, Takarazuka, Hyogo,

Japan 1 Assignw I l? nka reqs qrmsr991mm Yodogawa-ku, Osaka, Osaka- Prefecture, Japan [22] Filed: Dec. 6, 1971 [2]] Appl. No.: 204,861

[30] Foreign Application Priority Date Dec. 7, 1970 Japan ..45/l07597 [52] US. Cl ..3l7/26, 317/29 A, 307/85 [5 1] Int. Cl. ..H02h 7/26 [58] Field of Search..307/85, 86; 317/26, 29 R, 29 A [56] References Cited UNITED STATES PATENTS 2,005,136 6/1935 Evans et al. ..3l7/29 A 2,018,225 10/1935 Parsons ..3l7/29 A X Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Attorney-Elmer'R. Helferich et al.

[57] ABSTRACT A high tension network distribution system which comprises high voltage feeders connected in a nettype for carrying electric power of commercial frequency, distribution transformers connected to said feeders, feeder breakers at the ends of said feeders adjacent to the associated substation therefor, protector breakers at the ends of said feeders adjacent to their feeding points, a carrier signal transmitter for applying zero-phase-sequence carrier signals across said feeders and ground, an insulating transformer for transmitting said electric power of commercial frequency between adjacent feeders, but not for transmitting said carrier signal between the adjacent feeders, and signal receivers for receiving said zero-phase-sequence carrier signals from the feeders, said protector breakers including relay means for closing the corresponding breaker when the corresponding receiver receives the carrier signal and for opening the breaker when the receiver does not receive the carrier signal.

6 Claims, 4 Drawing Figures ike HIGH TENSION NETWORK DISTRIBUTION SYSTEM BACKGROUND OF THE INVENTION This invention relates to a network distribution system. The term low tension network system frequently used herein implies a network system where the low tension sides of distribution transformers are connected in a net type and the term high tension network system also frequently used herein implies a network system where the high tension sides of distribution transformers are connectedin a net type.

In the past, in order to serve heavy load density regions such as cities, factories and buildings with electric power with high reliance without service interruption, the so-called low tension network distribution system has been generally employed. However, in such a prior art system, the low tension sides of a plurality of distribution transformers respectively connected to different feeders are connected in a net type and generally, electric power is supplied from the distribution transformer connected to one feeder and the distribution transformer connected to the other feeder to the low voltage main line to which loads are connected. Such distribution transformers are generally referred to network transformers. When failure occurs in one feeder or the network transformer connected to the feeder, the low voltage main line is served with electric power only from the distribution transformer the lower tension side of which is connected to the main line whereas the high voltage side of which is connected to the other feeder. Therefore, the network or distribution transformers are required to have a larger current capacity than that conventional distribution transformers have and the conductors on the low voltage sides of the transformers are required to have a large current capacity accordingly. As a result, such a system requires to employ large size transformers and conductors having a large cross-section area which renders the system expensive with respect to installation, material cost and operation. Furthermore, the system has a complicate construction to such an extent that maintenance on the system becomes troublesome.

It has been well known that a high voltage network distribution system had been developed in the United States of America, but the system has not been practically employed in other countries. In such a system generally employed in the United States of America, a plurality of high voltage feeders are led from each of a plurality of unit substations and each of a plurality of distribution transformers is connected on the high voltage side thereof to each feeder from the plural unit substations. In other words, the high voltage or primary sides of the distribution transformers are connected to high voltage feeders which are connected in a net type. Since the primary side of each distribution transformer is connected to a plurality of feeders in this way, even if failure occurs in any one of the feeders, the distribution transformer is energized from the rest feeder or feeders. In such a system, in order to disconnect any one of the feeders from the main bus of the substation as failure occurs in the feeder, a feeder breaker is provided at the end of the feeder adjacent to the substation. And in order to disconnect the feeder in which failure occured from the net work, the end of the feeder adjacent to the feeding point thereof is provided with a network protector which is similar to that usually employed in a low tension network system. This protector includes a breaker which is adapted to open as electric power is reversely supplied from the other feeder. However, such a breaker is not desirable because the protector frequently tends to malfunction. Although the direction of electric power flowing through the protector is usually determined depending upon a particular phase relationship between the voltage and current employed, the electric current which flows through the feeder tends to lag or advance in phase with respect to the voltage due to the line impedance even if no failure occurs in the feeder. And also when there appears a component corresponding to a generator on the load side, the current to voltage phase relationship frequently varies substantially. In such a case, the protector operates inadvertently thereby to disconnect its feeder from the distribution transformer. In this way, the conventional high tension network distribution system has a disadvantage that the feeder is inadvertently disconnected.

Therefore, one principal object of the present invention is to provide a high tension network distribution system in which only when failure has occured in one of the feeders, the particular feeder is disconnected from the distribution system.

Another object of the present invention is to provide a high tension network distribution system of the above type in which feeders can be individually disconnected from the distribution system.

According to the present invention, there has been provided a high tension network distribution system which comprises aplurality of high voltage feeders connected to each other in a net type for carrying electric power of commercial frequency; a plurality of distribution transformers connected to feeding points of said feeders; a feeder breaker provided at the end of each of said feeders adjacent to the associated substation; a protector breaker provided at the end of each of said feeders adjacent to the feeding point; a carrier signal transmitter adapted to apply a zero-phasesequence carrier signal having a frequency different from said commercial frequency across said feeders and ground; an insulating transformer connected between adjacent ones of said feeders for transmitting said electric power of commercial frequency between said adjacent feeders, but not for transmitting said zero-phasesequence carrier signal between the feeders; and a plurality of signal receivers each adapted to receive said zero-phase-sequence carrier signal from the associated feeder, said receiver including relay means for closing said breaker when the receiver receives said carrier signal and for opening the breaker when the receiver receives no carrier signal.

The above and other objects and attendant advantages of the present invention will be more readily apparent to those skilled in the art from a reading of the following detailed description referring to the accompanying drawing which shows preferred forms of the invention for illustration purpose only, but not for limiting the scope of the same in any way.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of one preferred embodiment of three-phase three-wire type high tension network distribution system according to the present invention showing three conductors in the line of the system as one wire generally;

FIG. 2 is a schematic diagram of a carrier signal generator which transmits zero-phase-sequence control signals adapted to be applied across individual wires and a common ground in said distribution system of FIG. 1 and carried through the wires to the system;

FIG. 3 is a schematic diagram of a carrier signal receiver which receives a carrier signal at one point in the distribution system of FIG. 1; and

FIG. 4 is a schematic diagram of another embodiment of high tension network distribution system according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION The present invention will be now described referring to the accompanying drawing and more particularly, to FIG. 1 thereof in which three conductors in the line of one or first preferred embodiment of threephase three-wire high tension network distribution system of the invention are shown as one wire generally. Numeral 1 denotes a main bus which transmits three-phase electric power from one unit substation. It will be easily occured to those skilled in the art that the main bus 1 comprises three conductors. A plurality of high voltage feeders are branched off the main bus 1 and lead to distribution transformers as will be described hereinbelow. It will be appreciated that each of these feeders also comprises three conductors. Although only two feeders 32 and 42 are shown in the drawing, it will be appreciated that in fact more feeders may be employed.

The ends of the feeders 32 and 42 adjacent to the main bus 1 are provided with feeder breakers 31 and 41, respectively, which are provided in the unit substation. Each of the feeder breakers 31 and 41 is actuated in a conventional manner by an overcurrent relay 38 or 48 which is excited as failure current is allowed to flow through the associated feeder. The end of each of the feeders 32 and 42 adjacent to the feeding point is provided with a protector breaker 33 or 43. The protector breaker is actuated by a carrier control signal receiver 37 or 47 which includes a relay means adapted to be excited as transmission of any breaker controlling signal or carrier control signal to the associated feeder terminates. Details of the control signal receiver will be described hereinbelow.

The main bus 1 is provided with a carrier generator or transmitter 2 which supplies carrier control signals to the feeders 32 and 42. These carrier control signals are high frequency zero-phase-sequence signals to be applied to a zero-phase-sequence circuit between the three conductors of the main bus 1 and the ground.

As shown in FIG. 2, the carrier transmitter 2 comprises a signal oscillator 12 for generating high frequency signal, a voltage stabilizer 11 for stabilizing the high frequency signal from the oscillator and an amplifier 13 for amplifying the high frequency signal from the oscillator. The output of the amplifier 13 has the frequency of 1 kHz, and the voltage of volts, for example. The high frequency carrier signal is injected through three insulating capacitors l5 and interruption switches 16 respectively in series connected to the respectively associated capacitors.

There are provided receivers 37 and 47 which are respectively adapted to receive carrier control signals which are carried through the feeders 32 and 42, respectively and these receivers are identical with each other. Details of one of the receivers are shown in FIG. 3. The receiver comprises a receiver winding 22 connected between two conductors selected from the conductors of the associated feeder, an insulating capacitor 23 having one end connected to an intermediate point of the winding 22 and a reactor 24 having one end connected .to the other end of the capacitor the other end of which is grounded. The capacitor 23 and reactor 24 are set to resonant with the carrier frequency. Connected across the reactor 24 is a band-pass filter 25 which is adapted to remove any commercial frequency component undesirably included in a carrier signal developed across the reactor 24. After having passed through the filter 25, the carrier signal is passed through an A.C. amplifier to be amplified thereby and the resultant amplified carrier signal is supplied to a level detector 27 which is adapted to compare the level of the carrier signal with noise level and generate a first signal when the level of the carrier signal is higher than the noise level and generate a second signal when the level of the carrier signal is lower than the noise level.

The protector breaker 33 comprises a breaker closing relay 39 and a breaker tripping relay 39'. Similarly, the protector breaker 43 comprises a breaker closing relay 49 and a breaker tripping relay 49. In FIG. 1, these relays associated with the protective breaker 33 are generally shown by numeral 30 and the relays associated with the protective breaker 43 are generally shown by numeral 40. The breaker closing relay 39 or 49 is exited by the first signal from the level detector 27 of the receiver 37 or 47 and closes the breaker 33 or 43. On the other hand, the breaker tripping relay 39' or 49' is excited by the second signal from the level detector and opens the protector breaker 33 or 43. From the foregoing, it will be appreciated that when carrier signal is present in the high voltage feeder, the protector breaker is closed and when no carrier signal is present in the high voltage feeder, the protector breaker is open. It will be also appreciated that the plural feeders have only to be supplied with one type of signal and the signal can interrupt the protector breakers of the respective feeders.

The feeders 32 and 42 are respectively connected to high voltage network buses 34 and 44, respectively which each also comprises three conductors and adjacent network buses are connected to each other by a three-phase insulating transformers 5. Thus, it will be appreciated that the feeders or network buses are connected to each other in a net like by means of the transformer or transformers. The transformer transmits electric power of commercial frequency from one of adjacent network buses to the other, but does not transmit carrier signal. Therefore, it will be appreciated that when the feeder breaker of one of the feeders is interrupted to open the protector breaker associated with the particular feeder, carrier signal present in the other feeder will not be supplied to the first-mentioned feeder whereby the protector breaker of the first-mentioned feeder can be positively interrupted.

Thus, since the insulating transformer 5 functions to transmit electric power of commercial frequency from one of adjacent feeders to the other while blocking the carrier signal, both the windings of the transformer may have the same number of turns. However, for various reasons, there is an instance in which the impedance as seen on one side of the transformer is different from that as seen on the other side of the transformer. In such a case, both the transformer windings may be provided with taps for the purpose of compensating for difference between the impedances. One is respectively selected from the taps on both the windings so that such difference between the two impedances can be compensated for.

Connected to the respective network buses are the primary or high voltage windings of plural distribution transformers 35 and 36 or 45 an 46, respectively and the secondary or low voltage windings of the respective distribution transformers are adapted to serve consumers with electric power in a conventional manner. It will be appreciated that these distribution transformers need not have such a large capacity more than that necessary for the consumers. Under normal conditions, the distribution transformers 35 and 36 or 45 and 46 are respectively supplied with electric power from the respectively associated feeder 32 or 42.

In operation, assuming that failure has occured in the high voltage feeder 32, for example, now, the overcurrent relay 39 is excited to trip or open the feeder breaker 31. And now, the failure current also flows through the insulating transformer 5 to the adjacent feeder 42. However, the electric current flowing through the feeder 42 is restricted to a small value by the leakage impeadance of the insulating transformer 5, the overcurrent relay on the feeder 42 will not be excited. As mentioned hereinabove, since the zerophase-sequence carrier signal flowing through the feeder 42 is not transmitted to the feeder 32 by the insulating transformer 5, when the feeder breaker 31 is opened, there is no zero-phase-sequence carrier signal present in the feeder 32. Thus, the tripping relay 39' (FIG. 3) is excited to trip or open the protector breaker 33 whereby the feeder 32 in which the failure occured is disconnected from the network. On the other hand, since the distribution transformers 35 and 36 corresponding to the feeder 32 is supplied with electric power from the adjacent feeder 42 through the transformer 5, there will be no interruption of service occuring on the low voltage side of each of the transformers 35 and 36. When the feeder 32 restores from the failure, the feeder breaker 31 is again closed and as a result, the protector breaker 33 is also again closed to return to normal conditions.

Turning now to FIG. 4, there is shown another embodiment of the invention. In the embodiment of FIG. 4, an insulating transformer 5, comprises two primary windings 53 and 54 respectively connected through the respective protector breakers 33 and 43 to two adjacent feeders 32 an 42, respectively and one secondary winding 51 to which a plurality of distribution transforemers 35, 36, 45 and 46 are connected. The operation of the arrangement of FIG. 4 is exactly the same as described in connection with the first embodiment hereinabove.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, the invention can be also applicable to a high voltage network distribution system in which the feeders 32 and 42 are connected to different substations, for example. Therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A high tension network distribution system which comprises a plurality of high voltage feeders connected to each other in a net-type for carrying electric power of commercial frequency; a plurality of distribution transformers each connected to the feeding point of each of said feeders; a feeder breaker provided at the end of each of said feeders adjacent to its associated substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply a zero-phasesequence carrier signal having a frequency different from said commercial frequency across said feeders and ground; an insulating transformer for transmitting said electric power of commercial frequency between adjacent ones of said feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phase-sequence carrier signal from the associated feeder, said protector breaker including relay means for closing the cor responding breaker when said corresponding receiver receives said carrier signal and for opening the breaker when the receiver does not receive said carrier signal.

2. The system as set forth in claim 1, in which said insulating transformer has a first winding connected to one of said adjacent feeders and a second winding connected to the other of the adjacent feeders and said first and second windings are magnetically bonded to each other.

3. The system as set forth in claim 2, in which said first and second windings of the insulating transformer have the same number of turns.

4. The system as set forth in claim 2, in which said first and second windings of the insulating transformer have taps mounted thereon and said taps on the first and second windings are so selected that difference between impedances as seen on the opposite sides of said transformer can be compensated for.

5. A high tension network distribution system which comprises a plurality of high voltage feeders connected to each other in a net-type for carrying electric power of commercial frequency, said feeders being connected to a common substation; a feeder breaker provided at the end of each of said feeders. adjacent to said substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply zero-phasesequence carrier signal different from said commercial frequency across said feeders and ground; an insulating transformer connected between adjacent ones of said feeders for transmitting said electric power of commercial frequency between said adjacent feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phasesequence carrier signal from the associated feeder, said protector breaker including relay means for closing the corresponding breaker when the corresponding receiver receives said carrier signal and for opening the breaker when the receiver does not receive the carrier signal.

6. A high tension network distribution system which comprises a plurality of feeders connected to each other in a net-type for carrying electric power of commercial frequency, adjacent ones of said feeders being connected to different substantions; a feeder breaker provided at the end of each of said feeders adjacent to the associated substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply zero-phase-sequence carrier signal having a frequency different from said commercial frequency across said feeders and ground; an insulating transformer connected between adjacent ones of said feeders for transmitting said electric power of commercial frequency between adjacent ones of said feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phasesequence carrier signal from the associated feeders, said protector breaker including relay means for closing the corresponding breaker when said corresponding receiver receives said carrier signal and for opening the breaker when the receiver does not receive the carrier signal. 

1. A high tension network distribution system which comprises a plurality of high voltage feeders connected to each other in a net-type for carrying electric power of commercial frequency; a plurality of distribution transformers each connected to the feeding point of each of said feeders; a feeder breaker provided at the end of each of said feeders adjacent to its associated substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply a zero-phase-sequence carrier signal having a frequency different from said commercial frequency across said feeders and ground; an insulating transformer for transmitting said electric power of commercial frequency between adjacent ones of said feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phase-sequence carrier signal from the associated feeder, said protector breaker including relay means for closing the corresponding breaker when said corresponding rEceiver receives said carrier signal and for opening the breaker when the receiver does not receive said carrier signal.
 2. The system as set forth in claim 1, in which said insulating transformer has a first winding connected to one of said adjacent feeders and a second winding connected to the other of the adjacent feeders and said first and second windings are magnetically bonded to each other.
 3. The system as set forth in claim 2, in which said first and second windings of the insulating transformer have the same number of turns.
 4. The system as set forth in claim 2, in which said first and second windings of the insulating transformer have taps mounted thereon and said taps on the first and second windings are so selected that difference between impedances as seen on the opposite sides of said transformer can be compensated for.
 5. A high tension network distribution system which comprises a plurality of high voltage feeders connected to each other in a net-type for carrying electric power of commercial frequency, said feeders being connected to a common substation; a feeder breaker provided at the end of each of said feeders adjacent to said substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply zero-phase-sequence carrier signal different from said commercial frequency across said feeders and ground; an insulating transformer connected between adjacent ones of said feeders for transmitting said electric power of commercial frequency between said adjacent feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phase-sequence carrier signal from the associated feeder, said protector breaker including relay means for closing the corresponding breaker when the corresponding receiver receives said carrier signal and for opening the breaker when the receiver does not receive the carrier signal.
 6. A high tension network distribution system which comprises a plurality of feeders connected to each other in a net-type for carrying electric power of commercial frequency, adjacent ones of said feeders being connected to different substantions; a feeder breaker provided at the end of each of said feeders adjacent to the associated substation; a protector breaker provided at the end of each of said feeders adjacent to its feeding point; a carrier signal transmitter adapted to apply zero-phase-sequence carrier signal having a frequency different from said commercial frequency across said feeders and ground; an insulating transformer connected between adjacent ones of said feeders for transmitting said electric power of commercial frequency between adjacent ones of said feeders, but not for transmitting said zero-phase-sequence carrier signal between the adjacent feeders; and a plurality of signal receivers each adapted to receive said zero-phase-sequence carrier signal from the associated feeders, said protector breaker including relay means for closing the corresponding breaker when said corresponding receiver receives said carrier signal and for opening the breaker when the receiver does not receive the carrier signal. 